If you believe the conspiracy theorists, HAARP is a "death ray", it can cause earthquakes, control weather, bring down aircraft . . . even cause buildings to disintegrate. But as we shall see, HAARP, the High Frequency Active Auroral Research Program facility in Alaska is a highly useful and promising research centre.

By Dr David Maddison

All radio enthusiasts, whether they are amateurs, shortwave listeners or DX TV enthusiasts, know that the ionosphere has a large influence on radio propagation.

For example, long-range radio communication relies on reflection or refraction of radio signals by the ionosphere to achieve range.

Without the ionosphere radio signals would continue in a straight line path out into space and would not reach a receiver located beyond the horizon.

Communications enabled by and affected by the ionosphere include those to and from transoceanic aircraft flights and ship-to-shore, international shortwave broadcasts, amateur radio and military communications, over-the-horizon radar and many others.

Signals that must travel through the ionosphere, such as those from GPS and other satellites, can also be affected.

In the case of GPS signals, errors are introduced to positional fixes due to random variations in the ionosphere. Because these are small, they’re usually of no relevance to civilian GPS users. But they are important to users who require extremely high accuracy.

Unfortunately, the ionosphere is neither stable nor completely predictable and its properties are constantly varying according to the time of day, the season. the 11-year sunspot cycle and other solar activity.

An example of ionospheric variation that is familiar to most people is that medium wave (MW) radio broadcast signals are carried much further at night than during the day. But changes in the ionosphere can occur extremely rapidly, even at time scales of as little as a second.

“Space weather”

Space weather refers to changes in the space environment, particularly the region between the Earth and Sun. The “solar wind” from the Sun streams past the Earth and is mostly deflected by the Earth’s magnetic field but variations in the solar wind cause changes in the Earth’s magnetic field.

Ionogram generated by digisonde with frequency along the horizontal axis and
height in kilometres along the vertical axis. The coloured dots of the scatter plot
indicate the altitude at which signals of a given frequency are reflected by the ionosphere and correspond to its various layers. The black solid and dotted line
represents the electron density, which is related to the reflectivity of the ionosphere.

Quite regularly, from about once per week up to a few times per day, a solar flare is produced on the Sun which is generated by a tremendous release of magnetic energy and results in the emission of X-rays and UV rays. These can interact with the ionosphere if the emission is directed toward the Earth.

In addition, electrons, protons, heavy ions and atoms may be simultaneously ejected from the Sun (called a coronal mass ejection event) and impact upon the Earth’s magnetosphere. This can result in spectactular polar auroras. Also protons, which are travelling at up to about about one third of the speed of light, can constitute a serious radiation hazard for spacecraft and their occupants as well as a lesser hazard to aircraft.

When a solar flare interacts with the Earth’s atmosphere it can also result in damage to electrical power grids.

Here in Australia, from its office in central Sydney, the Ionospheric Prediction Service (IPS) monitors and forecasts space weather conditions, which include solar activity and geophysical and ionospheric conditions. Large numbers of radio users rely on the IPS data for their day-to-day radio operation. This government agency, (which now comes under the Bureau of Meteorology) has provided this service since 1947 (see www.ips.gov.au).